Flare-measuring mask, flare-measuring method, and exposure method

ABSTRACT

A method for measuring flare information of a projection optical system includes arranging, on an object plane of the projection optical system, a sectoral pattern surrounded by a first side, a second side which is inclined at a predetermined angle with respect to the first side, and an inner diameter portion and an outer diameter portion which connect both ends of the first side and both ends of the second side; projecting an image of the sectoral pattern via the projection optical system; and determining the flare information based on a light amount of the image of the sectoral pattern and a light amount provided at a position away from the image. With the flare measuring method, it is possible to correctly measure the flare information in an arbitrary angle range of the sectoral pattern.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. ProvisionalApplication No. 61/202,475 filed on Mar. 3, 2009, the entire disclosuresof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flare-measuring method for measuringflare information of a projection optical system, a flare-measuring maskusable to carry out the flare-measuring method, a maskpattern-correcting method using the flare-measuring method, and anexposure method using the flare-measuring method.

2. Description of the Related Art

In an exposure apparatus which is used in the photolithography step ofproducing various devices (electronic devices) including semiconductordevices, etc., if a scattered light, which is generated due to thesurface roughness of an optical member constructing a projection opticalsystem, forms any flare as a blur of an image around the image to beimaged by the genuine light flux, then the contrast of the image islowered, and the imaging characteristic is affected thereby.Accordingly, the flare of the projection optical system is measuredbeforehand; and for example, a shape of a pattern of a reticle (mask) iscorrected depending on a result of the measurement to form a targetpattern on a wafer (or a glass plate or the like) as the exposureobjective. In the case of an exposure apparatus (EUV exposure apparatus)which uses, as the exposure light (exposure light beam), an extremeultraviolet light or extreme ultraviolet light beam (hereinafterreferred to as “EUV light”) having a wavelength of not more than about100 nm, almost all of optical members including the reticle arereflecting members, wherein the flare tends to appear with ease, whilethe required resolution is heightened. Therefore, it is necessary tomeasure the flare highly accurately.

The Kirk method is known as a conventional flare-measuring method,wherein an image of an evaluating pattern, which includes, for example,an annular or zonal transmitting portion (or reflecting portion), issubjected to the exposure via a projection optical system, and the flareis evaluated based on the ratio of an exposure amount provided when animage of the transmitting portion is subjected to the exposure withrespect to an exposure amount provided when a center of an image of alight shielding portion disposed inside the transmitting portion issubjected to the exposure (see, for example, Japanese Patent ApplicationLaid-open No. 2007-234716). Recently, in order to further evaluate theflare in each of distinct directions, a flare-measuring method has beenalso suggested, wherein pairs of bar-shaped patterns are arranged whilebeing directed or oriented in four different directions, and the flareamount is determined for an image of a central gap portion of each ofthe pairs of bar-shaped patterns directed in one of the differentdirections (see, for example, Japanese Patent Application Laid-open No.2008-288338).

According to the conventional flare-measuring method in which the pairsof bar-shaped patterns are arranged while being directed or oriented inthe different directions, it is possible to compare the differences(anisotropies) in the distinct directions of the flares. However, evenif a large number of the pairs of bar-shaped patterns are arranged whilebeing directed in the different directions, a problem arises such thatan area, at which no bar-shaped pattern is arranged, is increased atpositions away or separated farther from the measuring point on theimage plane, and it is difficult to evaluate the contribution of theflare in relation to all directions.

SUMMARY OF THE INVENTION

Taking the foregoing circumstances into consideration, an object of thepresent invention is to provide a flare-measuring technique which makesit possible to correctly measure the flare information in an arbitraryangle range, a mask pattern-correcting technique using theflare-measuring technique, and an exposure technique using theflare-measuring technique.

According to a first aspect of the present invention, there is provideda flare-measuring mask comprising at least one aperture pattern having afirst straight line portion, a second straight line portion which isinclined at a predetermined angle with respect to the first straightline portion, and a first connecting portion which connects one end ofthe first straight line portion and one end of the second straight lineportion.

According to a second aspect of the present invention, there is provideda flare-measuring mask having a predetermined pattern and used tomeasure a flare of an optical system from an image of the predeterminedpattern which is projected via the optical system by being irradiatedwith a radiation, wherein the predetermined pattern includes: a firstarea which is extended in a radial direction from a predeterminedposition away from a rotational center in the radial direction and whichis spread about the rotational center at a predetermined opening angle;a second area which has a shape same as that of the first area and whichis arranged symmetrically to the first area with respect to therotational center; and a block area including the rotational center,located between the first and second areas and having an oppositecharacteristic regarding transmissivity or reflectivity with respect tothe radiation to that of the first and second areas.

According to a third aspect of the present invention, there is provideda flare-measuring method for measuring flare information of a projectionoptical system, the flare-measuring method comprising: arranging, on anobject plane of the projection optical system, an aperture patternhaving a first straight line portion, a second straight line portionwhich is inclined at a predetermined angle with respect to the firststraight line portion, and a first connecting portion which connects oneend of the first straight line portion and one end of the secondstraight line portion; irradiating (radiating) an exposure light ontothe aperture pattern and projecting an image of the aperture pattern viathe projection optical system; and determining the flare informationbased on a ratio of a light amount of the exposure light irradiated(radiated) onto the aperture pattern with respect to a light amount ofthe image of the aperture pattern provided via the projection opticalsystem.

According to a fourth aspect of the present invention, there is provideda flare-measuring method for measuring flare information of an opticalsystem, the flare-measuring method comprising:

arranging, on an object plane of the optical system, a mask including apredetermined pattern having: a first area which is extended in a radialdirection from a predetermined position away from a rotational center inthe radial direction and which is spread about the rotational center ata predetermined opening angle; a second area which has a shape same asthat of the first area and which is arranged symmetrically to the firstarea with respect to the rotational center; and a block area includingthe rotational center, located between the first and second areas andhaving an opposite characteristic regarding transmissivity orreflectivity with respect to a radiation to that of the first and secondareas;

irradiating the radiation onto the mask to project an image of thepattern via the optical system; and

determining the flare information by observing projected images of thefirst and second area or a projected image of the block area.

According to another aspect of the present invention, there is provideda mask pattern-correcting method for correcting a pattern, of a mask,which is to be projected by a projection optical system, the maskpattern-correcting method comprising: measuring flare information of theprojection optical system by the flare-measuring method of the presentinvention; and correcting the pattern based on a measurement result ofthe flare information.

According to still another aspect of the present invention, there isprovided an exposure method for illuminating a pattern or a pattern of apatterning mask with an exposure light or a radiation and exposing anobject with the exposure light via the pattern and a projection opticalsystem or an optical system, the exposure method comprising: measuringflare information of the projection optical system by theflare-measuring method of the present invention; correcting the patternas a transfer objective based on a measurement result of the flareinformation; and exposing the object with the exposure light via theprojection optical system and the corrected pattern as the transferobjective.

According to the flare-measuring method of the present invention, byprojecting the image of the aperture pattern, it is possible tocorrectly measure the flare information within a range of the openingangle (predetermined angle) of the aperture pattern and further toeasily process the measurement result on the polar coordinate system, ifnecessary.

According to the flare-measuring mask of the present invention, theaperture pattern thereof can be used when the flare-measuring method ofthe present invention is carried out.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a schematic construction of an exemplaryexposure apparatus according to an embodiment of the present invention.

FIG. 2A is a bottom view of an exemplary arrangement of a plurality ofevaluating patterns disposed on a test reticle, FIG. 2B is a magnifiedview of the evaluating pattern shown in FIG. 2A; and FIG. 2C is amagnified view to illustrate the shapes of sectoral patternsconstructing the evaluating pattern.

FIGS. 3A and 3B show a flow chart illustrating an exemplary operationfor measuring the flare of a projection optical system and correcting apattern of a reticle based on an obtained measurement result.

FIG. 4A is a plan view of images of the pattern of the test reticleexposed on a plurality of shot areas, respectively, on a wafer; FIG. 4Bshows a magnified plan view illustrating a part of a resist patternformed on the wafer after the development; FIG. 4C is a magnified planview illustrating a state that resist patterns corresponding to an imageof a pair of the sectoral patterns are connected to each other; and FIG.4D shows the flares in all of directions at a plurality of measuringpoints in an exposure area.

FIG. 5A shows an example of a Power Spectrum Density (PSD) in the radialdirection of the roughness of a mirror surface, and FIG. 5B shows anexample of a Point Spread Function (PSF) in the radial direction of theflare of the projection optical system.

FIG. 6 is magnified plan view illustrating an exemplary pattern afterthe correction of the reticle.

FIG. 7A is a magnified view illustrating a first modification of theevaluating pattern; FIG. 7B is a magnified view illustrating a secondmodification of the evaluating pattern; FIG. 7C is a magnified viewillustrating a third modification of the evaluating pattern; FIG. 7Dshows an image of the pattern shown in FIG. 7C; and FIG. 7E shows astate that the pattern shown in FIG. 7C is rotated.

FIG. 8 shows a flow chart illustrating exemplary steps of producing anelectronic device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An exemplary embodiment of the present invention will be explained withreference to FIGS. 1 to 6 by way of example.

FIG. 1 is a sectional view schematically illustrating the overallconstruction of an exposure apparatus 100 of this embodiment. Theexposure apparatus 100 is an EUV exposure apparatus which uses, as theexposure light (exposure light beam or illumination light (illuminationlight beam) for the exposure) EL, the EUV light (Extreme UltravioletLight) having a wavelength that is not more than about 100 nm and withina range of about 3 to 50 nm, for example, having a wavelength of 11 nmor 13 nm. With reference to FIG. 1, the exposure apparatus 100 includesa laser plasma light source 10 which pulse-generates the exposure lightEL, an illumination optical system ILS which illuminates a patternsurface (lower surface in this embodiment) of a reticle RC (mask) in anillumination area 27R with the exposure light EL, a reticle stage RSTwhich moves the reticle RC, and a projection optical system PO whichprojects an image of a pattern included in the illumination area 27R ofthe reticle RC onto a wafer W (photosensitive substrate) coated with aresist (photosensitive material). The exposure apparatus 100 furtherincludes a wafer stage WST which moves the wafer W, a main controlsystem 31 which includes a computer integrally controlling the operationof the entire apparatus; and the like.

In this embodiment, the EUV light is used as the exposure light(radiation) EL. Therefore, each of the illumination optical system ILSand the projection optical system (optical system) PO is constructed ofa plurality of catoptric optical members such as mirrors or the like,except for a specific filter or the like (not shown), and the reticle RCis also of the catoptric or reflecting type. The catoptric opticalmember has a reflecting surface obtained, for example, such that asurface of a member, which is composed of silica glass (or highly heatresistant metal or the like), is processed highly accurately into apredetermined curved surface or flat surface, and then a multilayeredfilm (reflective film for the EUV light), which is composed ofmolybdenum (Mo) and silicon (Si), is formed on the surface to providethe reflecting surface. The multilayered film may be anothermultilayered film obtained by combining a substance such as ruthenium(Ru), rhodium (Rh) or the like and a substance such as Si, beryllium(Be), carbon tetraboride (B₄C) or the like. The reticle RC is preparedas follows. That is, for example, a multilayered film is formed on asurface of a substrate made of silica glass to provide a reflectingsurface (reflective film). After that, a transfer pattern is formed onthe reflecting surface with an absorbing layer composed of a materialabsorbing the EUV light, including, for example, tantalum (Ta), nickel(Ni), chromium (Cr) and the like.

In order to avoid the absorption of the EUV light by a gas, the exposureapparatus 100 is accommodated in a box-shaped vacuum chamber 1approximately as a whole. For example, large-sized vacuum pumps 32A, 32Bare provided in order to perform the vacuum evacuation for the space inthe vacuum chamber 1, for example, via gas discharge tubes 32Aa, 32Ba.Further, a plurality of subchambers (not shown) are also provided inorder to further enhance the degree of vacuum on the optical path forthe exposure light EL in the vacuum chamber 1. For example, the vacuumchamber 1 has an internal gas pressure of about 10⁻⁵ Pa, and asubchamber (not shown), which accommodates the projection optical systemPO in the vacuum chamber 1, has an internal gas pressure of about 10⁻⁵to 10⁻⁶ Pa.

The following description will be made assuming that the Z axis extendsin the normal line direction of the surface (bottom surface of thevacuum chamber 1) on which the wafer stage WST is placed as shown inFIG. 1; the X axis extends perpendicularly to the sheet surface of FIG.1 in a plane perpendicular to the Z axis (plane substantially parallelto the horizontal surface in this embodiment); and the Y axis extends inparallel to the sheet surface of FIG. 1. In this embodiment, theillumination area 27R is formed on the reticle RC when the exposurelight EL is irradiated (radiated) onto the reticle RC. The illuminationarea 27R has a circular arc-shaped form which is long in the X direction(non-scanning direction) as shown in FIG. 2A. During the ordinaryexposure, the reticle RC and the wafer W are synchronously scanned inthe Y direction (scanning direction) with respect to the projectionoptical system PO.

At first, the laser plasma light source 10 is a light source of the gasjet cluster system including a high output laser light source (notshown); a light-collecting lens 12 which collects the laser beamsupplied from the laser light source via a window member 15 of thevacuum chamber 1; a nozzle 14 which jets a target gas of for example,xenon; and a light-collecting mirror 13 which has a spheroidalplane-shaped reflecting surface. The exposure light EL, which ispulse-emitted at a frequency of, for example, several kHz from the laserplasma light source 10, is focused or collected on the second focalpoint of the light-collecting mirror 13. The output of the laser plasmalight source 10 (radiation energy or irradiation energy of the exposurelight EL per unit time) is controlled by an exposure amount controlsystem 33 which is under the control of the main control system 31.

The exposure light EL, which is focused or collected on the second focalpoint, is substantially converted into a parallel light flux via aconcave mirror (collimator optical system) 21, and comes into a firstfly's eye optical system 22 constructed of a plurality of mirrors. Theexposure light EL, reflected by the first fly's eye optical system 22,comes into a second fly's eye optical system 23 constructed of aplurality of mirrors. An optical integrator is constructed by the pairof fly's eye optical systems 22, 23. The illumination light coming fromthe laser plasma light source 10 effects the Koehler illumination forthe first fly's eye optical system 22. The shapes, the arrangement, andother features of the respective mirror elements of the fly's eyeoptical systems 22, 23 are disclosed, for example, in U.S. Pat. No.6,452,661. The contents of U.S. Pat. No. 6,452,661 are incorporatedherein by reference.

With reference to FIG. 1, the reflecting surfaces of the respectivemirror elements of the first fly's eye optical system 22 aresubstantially conjugate with the pattern surface of the reticle RC; anda substantial surface light source (set or combination of a large numberof minute secondary light sources), which has a predetermined shape, isformed in the vicinity of the reflecting surface of the second fly's eyeoptical system 23 (in the vicinity of the light-exit surface of theoptical integrator). That is, a plane, on which the substantial surfacelight source is formed, is the pupil plane of the illumination opticalsystem ILS. An aperture diaphragm 28 is arranged at the pupil plane orat a position in the vicinity of the pupil plane to switch theillumination condition, for example, into the ordinary illumination, theannular illumination, the dipole illumination, or the quadrupleillumination.

The exposure light EL, passing through the aperture diaphragm 28, comesinto a curved mirror 24. The exposure light EL reflected by the curvedmirror 24 is reflected by a concave mirror 25. After that, the exposurelight EL illuminates the circular arc-shaped illumination area 27R ofthe pattern surface of the reticle RC obliquely from a lower position ata uniform illuminance distribution in a superimposed or overlay manner.A condenser optical system is constructed by the curved mirror 24 andthe concave mirror 25. The illumination optical system ILS isconstructed to include the concave mirror 21, the fly's eye opticalsystems 22, 23, the aperture diaphragm 28, the curved mirror 24, and theconcave mirror 25. In this case, the exposure light EL, which comes fromthe laser plasma light source 10, effects the Koehler illumination forthe first fly's eye optical system 22 as well as the pattern surface ofthe reticle RC. The illumination optical system ILS is not limited tothe construction shown in FIG. 1, and can be constructed in othervarious forms.

Further, a reticle blind (variable field diaphragm) is provided in orderto define the circular arc-shaped illumination area 27R with respect tothe pattern surface of the reticle RC. The reticle blind includes afirst Y axis blind 26Y1 which shields an outer (−Y direction) edgeportion of the exposure light EL, a second Y axis blind 26Y2 whichshields an outer (+Y direction) edge portion of the exposure light ELreflected by the reticle RC; and first and second X axis blinds (notshown) defining the position and the width in the X direction of theillumination area 27R with respect to the pattern surface of the reticleRC. The opening/closing operation of the reticle blind is controlled bya blind control system 34 which is under the control of the main controlsystem 31. The reticle blind of this embodiment forms a circulararc-shaped aperture (slit).

Further, the reticle RC is attracted and held on the bottom surface ofthe reticle stage RST via an electrostatic chuck RH. Based on themeasured value obtained by a laser interferometer (not shown) and acontrol information of the main control system 31, the reticle stage RSTis driven by a stage control system 35 at a predetermined stroke in theY direction via a driving system (not shown), which is constructed offor example a magnetically floating type two-dimensional linearactuator, along a guide surface parallel to the XY plane of the outersurface of the vacuum chamber 1, and the reticle stage RST is alsodriven in a minute amount, for example, in the X direction and adirection of rotation about the Z axis (OZ direction). The reticle RC isplaced (disposed) in the space surrounded by the vacuum chamber 1through an opening of the upper surface of the vacuum chamber 1. Apartition 8 is provided to cover the reticle stage RST on the side ofthe vacuum chamber 1. The interior of the partition 8 is maintained at agas pressure between the atmospheric pressure and a gas pressure in thevacuum chamber 1 by an unillustrated vacuum pump.

The exposure light EL, which is reflected by the illumination area 27Rof the reticle RC, is allowed to travel to the projection optical systemPO forming a reduction image of the pattern of the object plane (firstplane) on the image plane (second plane). The projection optical systemPO is constructed, for example, such that six mirrors M1 to M6 are heldby an unillustrated barrel; and the projection optical system PO is acatoptric system which is non-telecentric on the side of the objectplane (pattern surface of the reticle RC) and which is substantiallytelecentric on the side of the image plane (surface of the wafer W). Theprojection magnification is a reduction magnification of ¼-fold, etc.The exposure light EL, which is reflected by the illumination area 27Rof the reticle RC, forms the reduction image of a part of the pattern ofthe reticle RC in an exposure area 27W (area conjugate with theillumination area 27R) on the wafer W via the projection optical systemPO.

In the projection optical system PO, the exposure light EL from thereticle RC is reflected by the first mirror M1 in the upward direction(+Z direction). Subsequently, the exposure light EL is reflected by thesecond mirror M2 in the downward direction. After that, the exposurelight EL is reflected by the third mirror M3 in the upward direction,and the exposure light EL is reflected by the fourth mirror M4 in thedownward direction. Subsequently, the exposure light EL, which isreflected by the fifth mirror M5 in the upward direction, is reflectedby the sixth mirror M6 in the downward direction to form the image ofthe part of the pattern of the reticle RC on the wafer W. For example,the projection optical system PO is a coaxial optical system in whichthe optical axes of the mirrors, M1 to M6 are commonly overlapped withthe optical axis AX. An aperture diaphragm AS is arranged on the pupilplane disposed in the vicinity of the reflecting surface of the mirrorM2 or at a position in the vicinity of the pupil plane. A lightshielding mechanism is provided between the mirror M6 and the wafer W,which includes a pair of light shielding plates 30Y1 and 30Y2 in the Ydirection and a pair of light shielding plates in the X direction (notshown) in order to shield, for example, the flare generated by thescattering in the projection optical system PO. It is not necessarilyindispensable that the projection optical system PO is the coaxialoptical system. The projection optical system PO may be arbitrarilyconstructed.

Further, the wafer W is attracted and held on the wafer stage WST via anelectrostatic chuck WH. The wafer stage WST is arranged on a guidesurface arranged along the XY plane. Based on the measured valueobtained by a laser interferometer (not shown) and a control informationof the main control system 31, the wafer stage WST is driven by thestage control system 35 at predetermined strokes in the X direction andthe Y direction via a driving mechanism (not shown) constructed of, forexample, a magnetically floating type two-dimensional linear actuator,and the wafer stage WST is also driven in the θz direction, etc. ifnecessary.

An irradiation amount monitor 29, which is constructed of, for example,a photoelectric sensor such as a photodiode or the like having thesensitivity with respect to the EUV light, is arranged in the vicinityof the wafer W on the wafer stage WST. A detection signal of theirradiation amount monitor 29 is supplied to the main control system 31.For example, during the ordinary exposure, based on the measurementresult obtained by the irradiation amount monitor 29, the main controlsystem 31 controls the oscillation frequency and the pulse energy of thelaser plasma light source 10 via the exposure amount control system 33,and the main control system 31 controls, for example, the scanningvelocity of the reticle stage RST (and the wafer stage WST) via thestage control system 35 so that the totalized amount of exposure afterthe scanning exposure is included within an allowable range at each ofthe points on the wafer W. A data processing system 36, which performsthe data processing in relation to the flare measurement, is connectedto the main control system 31.

During the exposure, the wafer W is arranged in a partition 7 so that agas, which is generated from the resist on the wafer W, does not exertany harmful influence on the mirrors M1 to M6 of the projection opticalsystem PO. An opening, through which the exposure light EL is allowed topass, is formed in the partition 7. The space in the partition 7 isvacuum-evacuated by a vacuum pump (not shown) under the control of themain control system 31.

When one shot area (die) on the wafer W is exposed, the circulararc-shaped illumination area 27R is formed on the reticle RC by theillumination optical system ILS, and the reticle RC and the wafer W aresynchronously moved (subjected to the synchronous scanning) with respectto the projection optical system PO in the Y direction at apredetermined velocity ratio in accordance with the reductionmagnification of the projection optical system PO. In this way, one dieon the wafer W is exposed with the reticle pattern. After that, thewafer W is step-moved in the X direction and the Y direction by drivingthe wafer stage WST, and then the next shot area on the wafer W issubjected to the scanning exposure with the pattern of the reticle RC.In this way, the plurality of shot areas on the wafer W are successivelyexposed with the image of the pattern of the reticle RC in thestep-and-scan manner.

Next, an explanation will be made about the flare of the projectionoptical system PO of this embodiment. The scattered light, which is thefactor or main cause of the flare of the projection optical system PO,results from the surface roughness of each of the mirrors M1 to M6. Themagnitude or degree of the flare correlates with the surface roughnessPSD (Power Spectrum Density) which is the function of the power spectrumdensity exhibiting the magnitude or degree of the surface roughness,i.e., the function which relates to the magnitude or degree of theroughness with respect to the in-plane spatial frequency of the mirror.In particular, when the scattering angle is small, the surface roughnessPSD has a same shape as that of the flare PSF (Point Spread Function)which is the point intensity spread function brought about by the flare.The surface shape is two-dimensional. Therefore, PSD is originallytwo-dimensional as well. However, in a case that the anisotropy is nottaken into consideration, the rotational average is derived for thosehaving the same frequency to be dealt with as “radial PSD”.

The surface roughness radial PSD is in inverse proportion to the squareof the spatial frequency f with a proportional coefficient k, asfollows.radial PSD(f)≈k·f ⁻²  (1)

When the logarithms (log) of the both sides are taken, the followingexpression is obtained.log(radial PSD(f))≈−2·log f+log k  (2)

In this way, the radial PSD of the surface roughness is expressed by astraight line having an inclination or slope of −2 in the log scale.This is referred to as “fractal straight line”. The actual surface shapeis not ideal, and hence it is not coincident with the fractal straightline which is in inverse proportion to the square. However, it isempirically known that the approximation can be made for a good orsatisfactory polished surface with the function which is in inverseproportion to the square in a wide spatial frequency range. FIG. 5Ashows an example of the fractal straight line of the radial PSD [nm⁴] ofthe surface roughness. The horizontal axis in FIG. 5A is the spatialfrequency f [nm⁻¹].

When all of the roughnesses of the optical surfaces as described aboveare totalized in the projection optical system PO, it is possible toestimate the effective surface roughness possessed by the projectionoptical system PO (if the surfaces are dealt with as a single surface).The effective surface roughness PSDs is expressed by the following sumof products.PSDs(f)=Σαi×PSDi(αi·fi)  (3)

In the expression, i represents the number of the optical surface(mirror), PSDi represents the radial PSD of the ith mirror, firepresents the spatial frequency in relation to the ith mirror, and αirepresents the value of the ratio of the pupil diameter with respect tothe diameter of an area in which the pupil diameter is projected ontothe ith mirror. In accordance with the totalization as described above,the surface roughnesses of the respective mirrors are projected andsuperimposed on the pupil plane while being appropriately magnifiedand/or reduced, and the result is equivalent to that obtained if anoptical system, in which the resultant roughness exists on the pupilplane, is virtually assumed.

When the PSDs (f) is used, the flare PSF (r), which results from thesurface roughness, is expressed by the following expression.PSF(r)=(4π/(λ² z))² ·PSDs(r/(λz))  (4)

In the expression, r represents the distance on the wafer (distance ofarrival of the scattered light), λ represents the wavelength, and zrepresents the optical height of the pupil. PSD, which is the basis ofthe calculation, is the radial PSD. Therefore, the flare PSF is therotationally symmetric radial PSF as well. As also appreciated from theintroduction of the expression, all of the processes of calculation fromPSD to PSF are coupled or correlated by the linear transformation.Therefore, the surface roughness PSD and the flare PSF have a same shapeunder the predetermined approximation. This fact is described, forexample, in a reference “Christof Krautschik, et al.: Proceedings ofSPIE, (United States) Vol. 4688, p. 289 (2002)”.

FIG. 5B shows an example of the radial PSF [m⁻²] of the flare. In FIG.5B, the horizontal axis is the distance r [m] on the wafer.

The physical origin of the flare PSF is the surface roughness PSD. Thesurface roughness PSD has such a feature that the approximation can bemade by the fractal straight line which is in inverse proportion to thesquare of the spatial frequency f in the case of the radial PSD.Therefore, it is appropriate that the anisotropy of PSD is considered ineach of the orientations based on the degree of the deviation from thefunction which is in inverse proportion to the square of the spatialfrequency f, i.e., PSD is considered on the f-θ coordinate system (polarcoordinate system of the angle θ). In other words, it is appropriatethat the flare PSF is considered on the r-θ coordinate system (polarcoordinate system of the angle θ) as well. When the flare light isestimated, it is extremely easy to integrate the flare PSF on the polarcoordinate system as compared with a case in which the flare PSF isintegrated on the x-y coordinate system (rectangular coordinatessystem).

In view of the above, in this embodiment, the evaluating pattern for theflare is also based on the r-θ coordinate system, because the roughnessPSD is originally based on the f-θ coordinate system, and the flare PSFis based on the r-θ coordinate system.

That is, when the flare of the projection optical system PO is measured,the test reticle RT shown in FIG. 2A is loaded on the reticle stage RSTshown in FIG. 1, instead of the reticle RC. The test reticle RT isproduced by forming a reflective layer made of Mo/Si-multilayer film,etc. on a substrate made of a material through which the exposure lightis transmissive, for example, silica glass, low-thermal expansion glass,etc., and forming an absorbing layer PAB, for example tantalum nitride(TaN), tantalum germanium nitride (TaGeN), etc. which absorbs theexposure light on the reflective layer. The absorbing layer PAB definesan evaluating pattern with a part or parts (portion or portions) of theabsorbing layer being removed with a predetermined pattern, as will bedescribed later on.

As shown by a bottom view in FIG. 2A, three arrays of evaluatingpattern-forming portions 37A, 37B, 37C are set at predeterminedintervals in the X direction on the pattern area PA of the test reticleRT. Six evaluating patterns 4A, 4B, 4C, 4D, 4E, 4F, which have a sameshape and which have or are oriented in different directions, are formedat intervals L in the Y direction (in a scanning direction SD or in amovement direction) respectively, in each of the evaluatingpattern-forming portions 37A to 37C. The spacing distances between thecenters of the evaluating patterns 4A to 4F of the adjacent evaluatingpattern-forming portions 37A to 37C are not less than L. In a case thatthe outer diameter of each of the evaluating patterns 4A to 4F is aboutseveral 10 μm, the lower limit value of the distance L (details will bedescribed later on) is decreased in accordance therewith. Therefore, theevaluating patterns 4A to 4F may be arranged while being separated fromeach other approximately by the lower limit value of the distance L, forexample, in two arrays in the vicinity of a position approximatelyregarded as the same evaluation point in the pattern area PA.

Each of the evaluating patterns 4A to 4F is formed by a reflective layerhaving a predetermined pattern which is formed by removing a part orparts of the absorbing layer PAB with the predetermined pattern andwhich is exposed in the absorbing layer PAB, and each of the evaluatingpatterns 4A to 4F has a size accommodated in at least the width in the Ydirection of the illumination area 27R. In ordinary cases, a pluralityof the evaluating patterns (any one of 4A to 4F) can be arranged withinthe width in the Y direction of the illumination area 27R. In thisembodiment, the illumination area 27R is circular arc-shaped. Forexample, the position of the central evaluating pattern-forming portion37B is shifted or deviated in the Y direction so that the evaluatingpatterns (for example, 4A), which are directed in the same direction inthe respective evaluating pattern-forming portions 37A to 37C (or aplurality of the evaluating patterns included in the same arrangement),are simultaneously included in the illumination area 27R. Three or morearrays (for example, five arrays) of the evaluating pattern-formingportions may be provided in the pattern area PA. In a case that theevaluating patterns 4A to 4F are collectively arranged in the vicinityof the position which can be regarded as substantially the sameevaluation point, sets of evaluating patterns having shapes differentfrom those of the evaluating patterns 4A to 4F may be arranged in the Ydirection of the evaluating pattern-forming portions 37A to 37C.

As shown in a magnified view in FIG. 2B, one evaluating pattern 4A shownin FIG. 2A has a pair of sectoral patterns 3B-3A and 3B which have asame shape and which are arranged symmetrically in relation to a centralpoint 3C which serves as the rotational center. As shown in FIG. 2C, itis assumed that two straight lines LA, LB intersect with each other atan angle Δφ on the central point 3C. On this assumption, the onesectoral pattern (first area) 3A is a reflective pattern surrounded by afirst side 3Aa and a second side 3Ab which are disposed on the straightlines LA, LB, an inner diameter portion 3Ac which is disposed on acircumference having a radius r connecting ends (first ends), of thefirst side 3Aa and the second side 3Ab, disposed on the side of thecentral point 3C, and an outer diameter portion 3Ad which is disposed ona circumference having a radius R (>r) connecting ends, of the firstside 3Aa and the second side 3Ab, disposed on the outer side (secondends, of the first side 3Aa and the second side 3Ab, having a widerspacing distance therebetween than a spacing distance between the endsof the first side 3Aa and the second side 3Ab disposed on the side ofthe central point 3C, when the spacing distances between the both endsof the first side 3Aa and the second side 3Ab are compared with eachother). In other words, the sectoral pattern 3A is a sectoral reflectivepattern which is formed in the absorbing layer PAB and which has theopening angle of Δφ, the inner radius of r, and the outer radius of R.The sectoral pattern 3A can be considered as an area which is extendedfrom the central point 3C in the radial direction from a position ofdistance r (the position away from the central point 3C by the distancer) to a position of distance R (the position away from the central point3C by the distance R) and which is spread about the central point 3C atthe opening angle Δφ. On the other hand, the other sectoral pattern(second area) 3B is the identical pattern to the sectoral pattern 3A(symmetrical pattern to the sectoral pattern 3A with respect to thecentral point 3C) which is obtained by rotating the sectoral pattern 3Aby 180° about the central point 3C. Therefore, the pair of sectoralpatterns 3A, 3B can be also expressed as the pattern obtained byextracting the portions interposed between the two straight lines LA, LBfrom the bow tie-shaped pattern or the annular or zonal pattern. An area(block area) which includes the central point 3C exists between the pairof sectoral patterns 3A and 3B. In particular, small sectoral areas BLAand BLB are defined by the inner diameter portion 3Ac disposed on thecircumference on the radius r and the two straight lines LA and LB.

For example, in a case that the opening angle Δφ is small, the innerdiameter portion 3Ac (as well as the outer diameter portion 3Ad) can beapproximated by a straight line as well.

The opening angle Δφ of each of the sectoral patterns 3A, 3B is, forexample, 30°. In this case, the other evaluating patterns 4B, 4C, 4D,4E, 4F shown in FIG. 2A are obtained by rotating the pattern having thesame shape as that of the evaluating pattern 4A (sectoral patterns 3A,3B) about the central point by 30° (=Δφ), 60° (=2·Δφ), 90° (=3·Δφ), 120°(=4·Δφ), and 150° (=5·Δφ) respectively. Accordingly, the evaluatingpatterns 4A to 4F are arranged without any angle areas (angle ranges)overlapping with each other and without any gap in all of theorientations. Namely, although the evaluating patterns 4A to 4F have thesame opening angle Δφ, the evaluating patterns 4A to 4F are directed ororiented in the different directions respectively (the first side 3Aaand the second side 3Ab are extended in different directions among theevaluating patterns 4A to 4F). Further, the total of the opening anglesΔφ of the evaluating patterns 4A to 4F is 360°.

Each of the opening angles Δφ of the pair of sectoral patterns 3A, 3Bconstructing the evaluating pattern 4A may be, for example, 180°/m orthe supplementary angle thereof (=180°−180°/m) by using an integer m ofnot less than 2.Δφ=180°/m or −180°/m  (5)

In this case, those usable as the other evaluating patterns include m (mpairs of) evaluating patterns in which the sectoral patterns 3A, 3Bhaving the opening angles Δφ are arranged in orientations which aredifferent from each other by Δφ.

The spatial frequency f of the surface roughness PSD corresponds to thedistance r of the r-θ coordinate system of the flare PSF in relation tothe radius r of the inner diameter portion 3Ac and the radius R of theouter diameter portion 3Ad of each of the sectoral patterns 3A, 3B. Asshown in FIG. 5A, the spatial frequency f and the radial PSD are in therelationship represented by the straight line in the log scale.Therefore, it is most effective to equally divide the spatial frequencyf in the log scale. In other words, it is also effective to equallydivide the inner diameter or radius and the outer diameter or radius ofthe actual pattern in the log scale. For example, it is assumed that theminimum distance of the inner radius r is 1 μl and the maximum distanceof the outer radius R is 1 mm at the stage of the images of the sectoralpatterns 3A, 3B brought about by the projection optical system PO. Onthis assumption, the range has three digits. For example, the sectoralpatterns 3A, 3B having various shapes, which have radii r and R obtainedby equally dividing the same appropriately in the log scale, may beformed beforehand in the pattern area PA of the test reticle RT shown inFIG. 2A. Alternatively, such sectoral patterns may be formed beforehandwhile being separated into those disposed on a plurality of testreticles.

For example, when one digit is equally divided into four, a series ofvalues of the respective radii r, R to be prepared are, for example, 1μm, 1.8 μm, 3.2 μm, 5.6 μm, 10 μm, 18 μm, 32 μm, 56 μm, 100 μm, 180 μm,320 μm, 560 μm, and 1 mm. When the sets of radii r, R, which have thesizes or dimensions as described above and in which r<R is given, areselected, the band or zone of the spatial frequency f can be providedsubstantially equally in the log scale.

Further, the minimum value of the distance L between the centers of theevaluating patterns 4A to 4F shown in FIG. 2A is determined in order toperform the flare evaluation at a necessary evaluation accuracy by thefollowing method. It is assumed that the inner radius r is representedby a×R (a<1), the center-to-center distance L is represented by p×R(p>1), the number of the evaluating patterns 4A to 4F to be arrangedtherearound is N, and the maximum allowable value of the relative errorof the evaluation is e, by using the outer radius R of each of thesectoral patterns 3A, 3B of the adjacent evaluating patterns 4A, 4Bshown in FIG. 2A. On this, assumption, the relative error can be made tobe not more than e, provided that the spacing distance L (=p×R) betweenthe evaluating patterns is increased to effect the separation so thatthe parameter p is approximately in the following range.p>√{square root over ({N×(a ²−1)/(1.98×e×ln a)})}{square root over({N×(a ²−1)/(1.98×e×ln a)})}  (6)

When this relationship is used, if an adjacent evaluating patternadjacent to a certain evaluating pattern is of the same type (having thesame opening angle) as that of the certain pattern, and the adjacentevaluating pattern has any different size, then the relative error canbe made to be not more than e when the evaluating patterns are separatedfrom each other so that the parameter p is approximately in thefollowing range, for example, by using the outer radius R of the certainevaluating pattern (sectoral patterns 3A, 3B), assuming that the innerradius r is a×R (a<1), the outer radius R′ of the adjacent evaluatingpattern is c×R, the inner radius r′ is b×(c×R), the center-to-centerdistance L′ with respect to the adjacent evaluating pattern is p×R(p>1), the number of the evaluating patterns to be arranged therearoundis N, and the maximum allowable value of the relative error of theevaluation is e.p>c ²×√{square root over ({N×(b ²−1)/(1.98×e×ln a)})}{square root over({N×(b ²−1)/(1.98×e×ln a)})}  (7)

In a case that any large evaluating pattern is arranged at any fartherposition, it is necessary to slightly widen the spacing distance inconsideration of this fact as well. The foregoing parameter p can beapproximately calculated as follows.

It is now assumed that the inner radius r is a×R, the center-to-centerdistance L with respect to the adjacent evaluating pattern is p×R, andthe number of the adjacent evaluating patterns is N, by using the outerradius R of the evaluating pattern (sectoral patterns 3A, 3B). It is nowassumed that the evaluating pattern is not the evaluating patterns 4A to4F of this embodiment, but the evaluating pattern is a conventionallyused annular pattern. Further, it is assumed that the flare PSF isgenerally represented as follows by using a coefficient k.PSF(r)=k×r ⁻²  (8)

On this assumption, the flare amount F0, which is brought about by theevaluating pattern itself, is as follows.F0=2πk×ln(R/r)=2πk×ln a  (9)

The flare amount F from the surrounding pattern is approximately asfollows.F=N×β×2πk×ln((L+R)/(L−R))  (10)

In the expression, β represents the ratio of the area occupied by onecorresponding to one adjacent evaluating pattern in the annular arearanging from the radius (L−R) to the radius (L+R), which is expressed asfollows.β=π(R ² −r ²)/[π{(L+R)²−(L−R)²}]  (11)

On this condition, assuming that the allowable error e=F/F0 is given,the expressions (9) and (10) are applied thereto to obtain the followingrelationship.(1/p)ln((p+1)/(p−1))=4×e×R ²×ln a/{N×(R ² −r ²)}  (12)

It is affirmed that any case, in which a large error of not less than20% is permitted as the relative error, is ordinarily absent. Therefore,the left side of the expression (12) can be dealt with as the straightline approximation on the log scale approximately in a range of e<0.2.The expression (12) can be approximated as follows. The expression (6)is derived from the following expression.p ² e/N=−0.505(1−a ²)/ln a≈(a ²−1)/(1.98×ln a)  (13)

The above calculation is the case in which the adjacent evaluatingpattern is of the same type as that of the certain pattern. However,even in a case of any different type, the foregoing expression (7) canbe derived in accordance with the same or equivalent calculation. Evenwhen the certain pattern is the sectoral pattern 3A, 3B as in thisembodiment, if the opening angle of the certain pattern is the same asthat of the adjacent pattern, then the same area ratio is provided.Therefore, it is possible to use the same expression. If the openingangle of the certain pattern is different from that of the adjacentpattern, the adjustment may be made in relation to the expression byusing the number N of the surrounding evaluating pattern or patterns.

According to the above, for example, in a case that it is intended tosuppress the relative error to be not more than 1 (e=0.01), if eightpieces of identical evaluating patterns are arranged around the certainevaluating pattern, then p>15.5 is given assuming that the value of theratio a=r/R=0.2 is given between the inner radius and the outer radiusof the sectoral pattern 3A, 3B (for example, r is 2 μm and R is 10 μm).Therefore, the center-to-center distance L with respect to the adjacentevaluating pattern, which should be adopted, is not less than 155 μmwhich is 15.5 times the outer radius R of the pattern (7.7 times theouter diameter of the pattern). The area, which is disposedtherebetween, is the exclusive area in which any evaluating pattern(reflective pattern) should not be arranged. If the evaluating patternis arranged nearer to the above, there is such a possibility that therelative error cannot be suppressed to be not more than 1%.

In relation to the evaluation of the anisotropy of the flare on acertain image point evaluated as described above, it is necessary to payattention to the fact that the flare PSF corresponding to the imagepoint does not have the evaluated anisotropy. The flare is the amount ofthe irradiation of the flare PSF on another image point onto the certainimage point separated therefrom by a certain distance in a certainorientation. Therefore, the anisotropy of the flare, which is observedat a certain image point, merely is the observation of the difference inthe flare light arrived from another image point over a predetermineddistance at a predetermined angle. Therefore, in a case that the flarePSF at a certain image point is compared with the calculation result, itis necessary to recombine the data based on the evaluation results ofthe flare anisotropy in relation to a large number of image points in alarge number of orientations.

It is assumed that the opening angle Δφ is 30°, the radius r in thestate of the projected image is 1 μm, and the radius R is 5.6 μm in thestate of the projected image in relation to the pair of sectoralpatterns 3A, 3B of the evaluating pattern 4A shown in FIG. 2C. On thisassumption, it is possible to evaluate at the measuring point 39A of theexposure area 27W on the wafer shown in FIG. 4D, without any excess andany shortage, the flare in the range ranging from the distance 1 μm tothe distance 5.6 μm within each of the angle ranges 40A, 41A of ±15°about the center of the X axis. Similarly, by using the evaluatingpatterns 4B to 4F having the different orientations included in theevaluating pattern-forming portion 37A shown in FIG. 2A, it is possibleto evaluate at the measuring point 39A shown in FIG. 4D, without anyexcess and any shortage, the flare in the range ranging from thedistance 1 μm to the distance 5.6 μm within each of the correspondingangle ranges 40B to 40F and 41B to 41F respectively. Therefore, it ispossible to measure the flares in all of the directions without anyoversight or omission. Similarly, it is possible to measure the flaresin all of the directions without any oversight or omission, and it ispossible to correctly evaluate the anisotropy of the flare based on thedifference in the flare in each of the orientations at the othermeasuring points 39B, 39C shown in FIG. 4D by using the evaluatingpatterns 4A to 4F included in the other evaluating pattern-formingportions 37B, 37C shown in FIG. 2A.

With reference to FIG. 2A, it is assumed that other five evaluatingpatterns are present at the maximum around the evaluating patterns 4A to4F. On this assumption, the parameter p is larger than 11.9 according tothe expression (6). Therefore, it is appropriate that the distance Lbetween the centers of the evaluating patterns is increased to makeseparation by larger than 60 μm in the state of the projected image.Further, when a slight safety factor is taken into consideration, thenthe center-to-center distance is increased to make separation by 65 μm,and any reflective pattern may not be arranged therebetween at all.

The center-to-center distance L of the pattern, which is required, forexample, when the radius r of the sectoral pattern 3A, 3B is 1 μm andthe radius R is 100 μm, is p>7.4 according to the expression (6)assuming that the allowable relative error is 1% and the number ofevaluating patterns arranged therearound is 5. Therefore, thecenter-to-center distance may be increased to make separation by largerthan 740 μm in the state of the projected image.

Next, an explanation will be made with reference to a flow chart shownin FIGS. 3A and 3B about an example of the operation for evaluating theflare of the projection optical system PO of the exposure apparatus 100by using the test reticle RT shown in FIG. 2A. In this procedure, theoperation of the exposure apparatus 100 is controlled by the maincontrol system 31. At first, in Step 101 shown in FIG. 3A, the testreticle RT shown in FIG. 2A is loaded on the reticle stage RST shown inFIG. 1; and the alignment is performed for the test reticle RT by usingan alignment mark (not shown) of the test reticle RT. Subsequently, inStep 102, an unexposed wafer (referred to as “W”), which is coated witha positive type resist, is loaded on the wafer stage WST. Subsequently,in Step 103, the main control system 31 sets the exposure amount of thewafer to a predetermined lower limit value EP0 which is lower than thephotosensitive level of the resist, and 1 is given for the value of thecontrol parameter i. Subsequently, in Step 104, the exposure apparatus100 is used to expose a certain shot area 38A on the wafer W shown inFIG. 4A with images of the evaluating patterns 4A to 4F in the pluralityof directions included in the evaluating pattern-forming portions 37A to37C of the test reticle RT, in the preset exposure amount EP0. In thisprocedure, as shown in FIG. 2A, each of the portions of the pattern ofthe test reticle RT, which is illuminated with the illumination area27R, is subjected to the exposure in the preset exposure amount in thestep-and-repeat manner. For example, the images of the evaluatingpatterns 4A to 4F, which are included in each of the evaluatingpattern-forming portions 37A to 37C, are subjected to the exposure inthe vicinity of the predetermined measuring points 39A to 39C of theexposure area 27W shown in FIG. 4D respectively.

The images 4AP to 4FP of the evaluating patterns 4A to 4F are exposed onareas 37AP to 37CP, which correspond to the evaluating pattern-formingportions 37A to 37C on the shot area 38A on the wafer W shown in FIG.4A, in the Y direction respectively. Each of the images 4AP to 4FP isformed by images 3AP, 3BP of one of the pair of sectoral patterns 3A,3B. However, for the convenience of explanation, it is assumed that theimages of the patterns of the test reticle RT, which are erecting in theX direction and the Y direction, are formed on the wafer W. FIG. 2Ashows the bottom view illustrating the test reticle RT, and FIG. 4A isthe plan view illustrating the wafer W. Therefore, the both aresubjected to the inversion in the X direction.

Subsequently, in Step 105, it is judged whether or not the presetexposure amount arrives at the predetermined upper limit value (valuehigher than the level at which the resist is expected to be exposed withthe flare). At this stage, the exposure amount does not arrive at theupper limit value. Therefore, the operation proceeds to Step 106, andthe main control system 31 increases the exposure amount of the wafer bya predetermined amount ΔEP based on the following expression. Thepredetermined amount ΔEP is set depending on the measurement accuracyfor the flare.EPi=EP0+i·ΔEP  (14)

After that, 1 is added to the value of the parameter i in Step 107, andthen the ith shot area 38B (in this case, i=2) on the wafer W is exposedwith the images of the plurality of arrays of the evaluating patterns 4Ato 4F of the test reticle RT in the set exposure amount EPi. Theinformation about the set exposure amount EPI on the wafer W and thesequence (position) of the corresponding shot area is stored in the dataprocessing system 36. After that, for example, shot areas 38C, 38D onthe wafer W shown in FIG. 4A are exposed with the images of theplurality of arrays of the evaluating patterns 4A to 4F of the testreticle RT in the gradually increasing exposure amount EPi respectivelyuntil the set exposure amount EPi exceeds the upper limit value thereof.The three arrays of the areas 37AP to 37CP of the shot areas 38B to 38Dand other shot areas (not shown) on the wafer W are also exposed withthe images 4AP to 4FP of the evaluating patterns 4A to 4F respectively.If one wafer is insufficient for a number of the shot areas to besubjected to the exposure, a large number of the shot areas disposed ona plurality of wafers may be exposed with the images of the patterns ofthe test reticle RT in the gradually increasing exposure amount.

After that, if the set exposure amount EPi exceeds the upper limitvalue, the operation proceeds from Step 105 to Step 108; and the wafer Wis unloaded from the exposure apparatus 100, and the wafer W istransported to an unillustrated coater/developer. The resist of thewafer W is developed by the coater/developer. The resist pattern isformed by eliminating (dissolving) the portions corresponding to theimages 4AP to 4FP of the evaluating patterns 4A to 4F shown in FIG. 4A,for example, in each of the shot areas 38A to 38D on the wafer W afterthe development.

Subsequently, in Step 109, the wafer W after the development is set inan unillustrated scanning electron microscope (SEM) to determineinformation about the sequence of the shot areas provided when thegenuine image portions are exposed (eliminated) and information aboutthe sequence of the shot areas provided when the centers of the images4AP to 4FP (images of the central points 3C) are exposed (eliminated)for each of the images 4AP to 4FP of the evaluating patterns 4A to 4F inthe respective directions and for each of the areas 37AP to 37CP of, forexample, all of the shot areas 38A to 38D subjected to the exposure onthe wafer W shown in FIG. 4A. These informations are supplied to thedata processing system 36 shown in FIG. 1.

In this procedure, the case in which the genuine image of the evaluatingpattern 4A is representatively subjected to the exposure means that therecessed resist patterns 3AP, 3BP are formed at the positions of genuineimages 3AR, 3BR of the pair of sectoral patterns 3A, 3B constructing theevaluating pattern 4A as shown in FIG. 4B. On the other hand, the casein which the center of the image 4AP of the evaluating pattern 4A issubjected to the exposure means that the resist patterns 3AR, 3BR, whichcorrespond to the images 3AP, 3BP of the sectoral patterns 3A, 3B, aregradually widened due to the flare, and the resist patterns 3AR, 3BR areconnected to each other at the portion of an image 3CP of the centralpoint 3C of the sectoral patterns 3A, 3B as shown in FIG. 4C. Note thatin the case that the resist patterns 3AR, 3BR are connected to eachother at the portion of the image 3CP of the central point 3C of thesectoral patterns 3A, 3B, the image of the areas (block areas) BLA, BLBwhich are interposed between or sandwiched by the sectoral patterns 3A,3B of the evaluating pattern 4A does not appear, as shown in FIG. 4C. Insuch a case, it is not necessary that the images of the resist patterns3AR, 3BR maintain the sectral shapes as shown in FIG. 4C; and the imagesof the resist patterns 3AR, 3BR may be connected at the portion of theimage 3CP of the central point 3C such that the images of the resistpatterns 3AR, 3BR are widened as a whole. Namely, it is allowable thatthe resist patterns 3AR, 3BR are not formed to have the sectral shapes.

The data processing system 36 determines an exposure amount EPa providedwhen the portions of the genuine images are subjected to the exposureand an exposure amount EPb provided when the center of the images issubjected to the exposure due to the flare for each of the images 4AP to4FP of the evaluating patterns 4A to 4F in the respective directions foreach of the areas 37AP, 37CP, i.e., for each of the correspondingmeasuring points 39A to 39C in the exposure area 27W shown in FIG. 4D byusing the information about the sequence (positions) of the shot areasand the information about the exposure amount EPi provided when each ofthe shot areas is subjected to the exposure. Subsequently, in Step 110,the data processing system 36 calculates a flare amount Fc of theprojection optical system PO in accordance with the following expressionfor each of the evaluating patterns 4A to 4F and in each of thedirections for each of the measuring points 39A to 39C. That is, theflare amount Fc is calculated based on the ratio (value of the ratio) ofthe exposure amount EPa with respect to the exposure amount EPb.Fc=(EPa/EPb)×100(%)  (15)

Accordingly, the flare amount of the projection optical system PO isconsequently measured without any gap in each of the six directions 40A,41A to 40F, 41F for each of the measuring points 39A to 39C included inthe exposure area 27W.

Subsequently, in Step 111, the data processing system 36 calculates thecorrection amount for the shape including, for example, the line widthof the pattern of the reticle RC for the device shown in FIG. 1 based onthe flare amount Fc in each of the directions of the projection opticalsystem PO determined in Step 110.

For example, as shown in FIG. 6 in a magnified manner, it is assumedthat parts of the pattern on the reticle R, which is provided when theflare of the projection optical system PO is not considered, aredesignated as circuit patterns 42A to 42C. On this assumption, forexample, the correction amount for the line width or the like iscalculated in order to form a pattern having the shape as exactly formedto follow the designed value on the wafer in consideration of the flareamount in the corresponding direction for each of portions 42Aa, 42Ab,42Ac, 42Ad having different directions of the circuit pattern 42A. As aresult, for example, circuit patterns 43A to 43C, which are depicted bytwo-dot chain lines, are obtained as circuit patterns after thecorrection.

After that, in Step 112, a reticle (patterning mask) (also referred toas “RC”) is produced based on the correction amount obtained in Step111. Subsequently, in Step 113, the reticle RC after the correction isloaded on the reticle stage RST shown in FIG. 1 to perform the exposurefor the wafer W. Accordingly, it is possible to form the pattern asexactly shaped to follow the designed value on the wafer W, whilecorrectly considering the flare in each of the distinct directions ofthe projection optical system PO.

The function, the effect, etc. of this embodiment are as follows.

(1) The method for measuring the flare of the projection optical systemPO of the exposure apparatus 100 of this embodiment includes Step 101 ofarranging, on the object plane of the projection optical system PO, theevaluating pattern 4A composed of the sectoral pattern 3A (aperturepattern) formed (surrounded) by the first side 3Aa, the second side 3Abwhich is inclined at the angle Δφ with respect to the first side 3Aa,and the inner diameter portion 3Ac and the outer diameter portion 3Adwhich connect the both ends of the first side 3Aa and the both ends ofthe second side 3Ab, and the sectoral pattern 3B symmetrical to thesectoral pattern 3A; Step 104 of irradiating the exposure light onto theevaluating pattern 4A to project the image of the evaluating pattern 4Avia the projection optical system PO; and Steps 109 and 110 ofdetermining the flare information based on the ratio of the light amountof the exposure light irradiated onto the evaluating pattern 4A withrespect to the light amount of the image of the evaluating pattern 4Aprovided via the projection optical system PO.

The conventional flare-measuring method, in which the pairs ofbar-shaped patterns are arranged while being directed in the differentdirections, is such a method that the flare can be easily calculated onthe rectangular coordinates system. However, the conventionalflare-measuring method involves such a problem that the calculation iscomplicated on the polar coordinate system. In contrast to theconventional flare-measuring method, when the flare-measuring method ofthis embodiment is adopted, the flare information can be correctlymeasured within the range of the opening angle (predetermined angle) Δφof the sectoral patterns 3A, 3B constructing the evaluating pattern 4Aby projecting the image of the evaluating pattern 4A. Further, ifnecessary, the measurement result can be easily processed on the polarcoordinate system including, for example, the point intensity spreadfunction PSF (Point Spread Function).

It is allowable that only the sectoral pattern 3A is arranged on theobject plane of the projection optical system PO. In this case, it ispossible to measure the flare in the direction of the sectoral pattern3A.

(2) In this embodiment, the sectoral patterns 3A, 3B are symmetrical inrelation to the central point 3C which is the point of intersection ofthe straight lines LA, LB obtained by extending the first side 3Aa andthe second side 3Ab. Therefore, the flare can be easily evaluated bycomparing the exposure amount provided at the position of the image ofthe central point 3C with the exposure amount provided at the positionsof the images of the sectoral patterns 3A, 3B.

(3) In Step 102, the evaluating patterns 4B to 4F, each of which has thesame shape as that of the evaluating pattern 4A and which are arrangedin the different directions so that the angles are 360° in total, arealso arranged. In Steps 108 to 110, the flare of the projection opticalsystem PO is determined in each of the directions of the evaluatingpatterns 4A to 4F. Therefore, it is possible to measure the anisotropyof the flare of the projection optical system PO without any gap.

(4) The test reticle RT for measuring the flare of the embodimentdescribed above is formed with the evaluating pattern 4A composed of thesectoral pattern 3A and the sectoral pattern 3B symmetrical thereto.Therefore, the flare-measuring method described above can be carried outby using the test reticle RT.

At least one of the inner diameter portion 3Ac and the outer diameterportion 3Ad of each of the sectoral patterns 3A, 3B may be a straightline irrelevant to the largeness/smallness of the opening angle.

The inner diameter portion 3Ac of each of the sectoral patterns 3A, 3Bmay be omitted, and the first side 3Aa and the second side 3Ab maydirectly intersect with each other. In this case, when the outerdiameter portion 3Ad is a straight line, the sectoral patterns 3A, 3Bcan be dealt with as triangular patterns.

(5) The evaluating patterns 4A to 4F having the different directions areformed on the test reticle RT. Therefore, it is possible to measure theanisotropy of the flare of the projection optical system PO.

It is allowable that only one evaluating pattern 4A of the evaluatingpatterns 4A to 4F is formed beforehand on the test reticle RT shown inFIG. 2A. Alternatively, it is allowable that only two evaluatingpatterns (for example, 4A, 4B) of the evaluating patterns 4A to 4F areformed beforehand on the test reticle RT shown in FIG. 2A. Even in thiscase, it is possible to measure the flare in the direction of theevaluating pattern 4A (or in the directions of the evaluating patterns4A, 4B).

It is also allowable that one sectoral pattern 3A of the evaluatingpattern 4A is formed beforehand. Even in this case, it is possible tomeasure the flare in the direction of the sectoral pattern 3A.

(6) The test reticle RT has the reflective film which is provided on thesurface of the substrate and which reflects the exposure light, and theabsorptive film which is provided on the surface of the reflective filmand which absorbs the exposure light. Each of the evaluating patterns 4Ato 4F is formed as the reflective pattern obtained by removing a part ofthe absorptive film. Therefore, the test reticle RT can be used as thereflection type mask for the EUV exposure apparatus.

In this case, the substrate of the test reticle RT may be either atransmissive member through which the exposure light is transmitted or ametal member through which the exposure light is not transmitted.

In a case that the test reticle RT is used as the transmission typereticle for an exposure apparatus which uses an exposure light having awavelength of, for example, 193 nm, the test reticle has, for example, asubstrate through which the exposure light is transmissive, and a lightshielding film which is provided on the surface of the substrate. Theevaluating patterns, which correspond to the evaluating patterns 4A to4F, are formed as transmissive patterns (aperture patterns) eachobtained by removing a part of the light shielding film.

(7) The method for correcting the pattern of the reticle of thisembodiment includes Steps 101 to 111 of measuring the flare informationof the projection optical system PO by the flare-measuring method ofthis embodiment; and Step 112 of correcting the pattern based on themeasurement result of the flare information. Therefore, the pattern ofthe reticle can be corrected while taking the anisotropy of the flare ofthe projection optical system PO into consideration as well.

(8) The exposure method of this embodiment is the exposure method forilluminating the pattern of the reticle RC with the exposure light ELand exposing the wafer W via the pattern and the projection opticalsystem PO, which includes Steps 101 and 111 of measuring the flareinformation of the projection optical system PO by the flare-measuringmethod of this embodiment; Step 112 of correcting the pattern as thetransfer objective based on the measurement result of the flareinformation; and Step 113 of exposing the wafer W via the pattern afterthe correction and the projection optical system PO. Therefore, evenwhen the flare of the projection optical system PO is present, it ispossible to form the target pattern on the wafer W.

Next, a modification of the foregoing embodiment will be explained withreference to FIG. 7 (FIGS. 7A to 7E).

A test reticle TR shown in FIG. 7A has evaluating patterns 54A to 54Feach of which is composed of a pair of sectoral patterns 53A, 53B havingan opening angle Δφ1 (=180°−Δφ) as the supplementary angle as comparedwith each of the sectoral patterns 3A, 3B having the opening angle Δφshown in FIG. 2A, the evaluating patterns 54A to 54F being arranged inan absorbing layer PAB while being rotated by the angle Δφ. Assumingthat the opening angle Δφ is 30°, the opening angle Δφ1 of the sectoralpattern 53A, 53B is 150° which is five times the angle 30°. Therefore,the flare amount of the center of the images of the sectoral patterns53A, 53B is five times the flare amount of the center of the images ofthe sectoral patterns 3A, 3B. It is possible to greatly narrow thevariable range of the exposure amount. Therefore, it is possible toeasily measure the flare amount.

An exposure amount, which is provided when the resist is exposed(eliminated) at the center of the images of the sectoral patterns 53A,53B shown in FIG. 7A, is approximately equivalently about 6/5 of theexposure amount which is provided when the conventional annular patternis used, wherein the flare is measured with ease. Further, the openingangle Δφ1 of each of the sectoral patterns 53A, 53B is 150°, and theangle of the dark portion (absorbing layer PAB) disposed between thesectoral patterns 53A, 53B is 30°. Therefore, when the flare isevaluated by using the sectoral patterns 53A, 53B, it is possible toevaluate the flare in such a way that the influence of the flare, whichis to be exerted in any orientation disposed therebetween, is excluded.Therefore, the measurement result of the flare, which is obtained whenthe evaluating patterns 4A to 4F shown in FIG. 2A are used, can bedetermined from the measurement result of the flares with the evaluatingpatterns 54A to 54F having the six orientations.

Another evaluating pattern for a transmission type reticle is shown inFIG. 7B, wherein it is also allowable to form, in a light shieldingportion PAT, an evaluating pattern 56A which is composed of a pair ofsectoral patterns 55A, 55B having an opening angle of 90°, and anevaluating pattern 56B which has such a shape that the evaluatingpattern 56A is rotated by 90°.

Still another evaluating pattern is shown in FIG. 7C; wherein only onesectoral pattern 3A having an opening angle θφ may be formed as areflective layer in an absorbing layer PAB. In this case, it is assumedthat the image of the sectoral pattern 3A, which is formed by theprojection optical system PO, is an image 3AP shown in FIG. 7D. On thisassumption, a light-receiving surface 29 a of the irradiation amountmonitor 29 shown in FIG. 1 may be firstly set at a position D1 of thecenter of the image 3AP to measure a light amount OP1, and then thelight-receiving surface 29 a may be moved to a position D2 whichincludes the image 3CP of the central point 3C of the sectoral pattern3A to measure a light amount OP2. In this case, the flare amount in thedirection of the image 3AP of the sectoral pattern 3A is OP2/OP1×100(%).

In this case, a rotatable table (not shown) is provided on the reticlestage RST shown in FIG. 1, and the flare amount is measured whilerotating the sectoral pattern 3A by the angle Δφ respectively as shownin FIG. 7E. Accordingly, it is possible to measure the flare amount inall of the directions.

The sequence of the arrangement of, for example, the evaluating patterns4A to 4F and 54A to 54F shown in FIGS. 2 and 7 is not limited to thearrangement explained in this embodiment.

The light shielding mechanism, which includes the light shielding plates30Y1 and 30Y2 shown in FIG. 1 and the pair of light shielding plates inthe X direction (not shown), may be omitted. By doing so, it is possibleto measure the flare in a wide range not shielded by the light shieldingplates 30Y1 and 30Y2 and the pair of light shielding plates in the Xdirection.

The embodiment shown in FIG. 1 is illustrative of the case in which theEUV light is used as the exposure light, and the all reflectionprojection optical system constructed of only the six mirrors is used.However, this case is provided by way of example. The present inventionis also applicable, for example, to an exposure apparatus provided witha projection optical system constructed of, for example, only fourmirrors as a matter of course as well as to an exposure apparatusprovided with a projection optical system having, for example, four toeight mirrors while using the light source of a VW light source having awavelength of 100 to 160 nm, for example, the Ar₂ laser (wavelength: 126nm).

Further, the present invention is also applicable when a projectionoptical system, which is constructed of a dioptric system using, forexample, an ArF excimer laser beam (wavelength: 193 nm) as the exposurelight, is used.

In a case that an electronic device such as a semiconductor device (or amicrodevice) is produced by using the exposure method or the exposureapparatus of the embodiment described above, as shown in FIG. 8, theelectronic device is produced by performing, for example, a step 221 ofdesigning the function and the performance of the electronic device; astep 222 of manufacturing a mask (reticle) based on the designing step;a step 223 of producing a substrate (wafer) as a base material for thedevice and coating the substrate (wafer) with the resist; asubstrate-processing step 224 including a step of exposing the substrate(photosensitive substrate) with the pattern of the reticle by theexposure method and the exposure apparatus of the embodiment describedabove, a step of developing the exposed substrate, a step of heating(curing) and etching the developed substrate, etc.; a step 225 ofassembling the device (including processing processes such as a dicingstep, a bonding step, a packaging step, etc.); an inspection step 226;and the like.

Therefore, the method for producing the device includes forming thepattern of the photosensitive layer on the substrate by using theexposure method or the exposure apparatus of the embodiment describedabove, and processing the substrate formed with the pattern (Step 224).According to the exposure apparatus or the exposure method, it ispossible to reduce or mitigate the influence of the flare of theprojection optical system. Therefore, the electronic device can beproduced highly accurately.

The present invention is not limited to the application to theproduction process for the semiconductor device. The present inventionis also widely applicable, for example, to the production process for adisplay apparatus including, for example, a liquid crystal displayelement formed on a rectangular glass plate and a plasma display as wellas to the production process for various devices including, for example,an image pickup element (CCD, etc.), a micromachine, MEMS(Microelectromechanical Systems), a thin film magnetic head, and a DNAchip, and the mask itself or the like.

The present invention is not limited to the embodiments described above,which may be embodied in other various forms without deviating from thegist or essential characteristics of the present invention.

What is claimed is:
 1. A flare-measuring method for measuring flareinformation of a projection optical system, the flare-measuring methodcomprising: arranging at least one aperture pattern of a mask at anobject plane of the projection optical system, each aperture pattern ofthe at least one aperture pattern having a first straight line portion,a second straight line portion that is inclined at a predetermined anglewith respect to the first straight line portion, and a first connectingline portion that connects one end of the first straight line portionand one end of the second straight line portion; irradiating an exposurelight onto the at least one aperture pattern and forming an image of theat least one aperture pattern from the mask via the projection opticalsystem onto a photosensitive substrate at an image plane of theprojection optical system; and measuring flare information based on aratio of (1) a first light amount of the exposure light irradiated ontothe at least one aperture pattern to (2) a second light amount of theimage of the at least one aperture pattern provided via the projectionoptical system, wherein the at least one aperture pattern is defined bythe first straight line portion, the second straight line portion andthe first connecting line portion, and the arranging of the at least oneaperture pattern comprises arranging a plurality of pairs of theaperture patterns in a scanning direction of the projection opticalsystem, the plurality of pairs of the aperture patterns being orientedin mutually different rotation directions about a point of intersectionof a first straight line obtained by extending the first straight lineportion and a second straight line obtained by extending the secondstraight line portion.
 2. The flare-measuring method according to claim1, wherein the forming of the image of the at least one aperture patterncomprises projecting the image of the at least one aperture pattern fromthe mask onto different positions on the photosensitive substrate, whilechanging an exposure amount; and the measuring of the flare informationcomprises measuring the flare information based on a ratio of (i) afirst exposure amount provided when the photosensitive substrate beginsto be exposed at a portion that corresponds to the image of the at leastone aperture pattern from the mask formed via the projection opticalsystem to (ii) a second exposure amount provided when the photosensitivesubstrate is exposed at a portion that is in a predetermined positionalrelationship with respect to the image of the at least one aperturepattern from the mask formed via the projection optical system.
 3. Theflare-measuring method according to claim 1, wherein images of the pairsof aperture patterns are successively formed via the projection opticalsystem onto the photosensitive substrate, while moving the exposurelight in the predetermined direction relative to the pairs of aperturepatterns.
 4. The flare-measuring method according to claim 1, whereinthe arranging of the at least one aperture pattern further comprisesarranging a plurality of lines of the plurality of pairs of the aperturepatterns arranged in the scanning direction, in a directionperpendicular to the scanning direction.
 5. A mask pattern-correctingmethod for correcting a mask pattern, the mask pattern-correcting methodcomprising: measuring flare information of the projection optical systemby the flare-measuring method as defined in claim 1; and correcting themask pattern based on a measurement result of the flare information. 6.An exposure method for illuminating a pattern with an exposure light andexposing an object with the exposure light via the pattern and aprojection optical system, the exposure method comprising: measuringflare information of the projection optical system by theflare-measuring method as defined in claim 1; correcting the pattern asa transfer objective based on a measurement result of the flareinformation; and exposing the object with the exposure light via theprojection optical system and the corrected pattern as the transferobjective.
 7. The flare-measuring method according to claim 1, whereinthe arranging of the at least one aperture pattern comprises arranging afirst pair of the plurality of pairs of the aperture patternssymmetrically with respect to the point of intersection of the firststraight line the second straight line.
 8. The flare-measuring methodaccording to claim 7, wherein the plurality of pairs of the aperturepatterns have a same shape as that of the first pair of aperturepatterns; and the measuring of the flare information comprises measuringthe flare information for each of the rotation directions of each of theplurality of pairs of aperture patterns.
 9. The flare-measuring methodaccording to claim 7, wherein the point of intersection is arrangedbetween two aperture patterns constituting the first pair of theaperture patterns.
 10. A flare-measuring method for measuring flareinformation of an optical system, the flare-measuring method comprising:arranging, at an object plane of the optical system, a predeterminedpattern of a mask, the predetermined pattern having: a first area thatextends in a radial direction away from a rotational center, the firstarea starting at a predetermined position spaced away from therotational center and spreading at a predetermined opening angle as thefirst area extends away from the rotational center; a second area thathas a same shape as that of the first area and that is arrangedsymmetrically to the first area with respect to the rotational center;and a block area that includes the rotational center, located betweenthe first and second areas and having an opposite characteristicregarding transmissivity or reflectivity with respect to a radiation ascompared to that of each of the first and second areas; irradiating theradiation onto the mask to project and form on a photosensitivesubstrate at an image plane of the optical system an image of thepredetermined pattern via the optical system; and measuring flareinformation either by observing projected images of the first and secondareas or by observing a projected image of the block area, wherein thearranging of the predetermined pattern comprises arranging a pluralityof the predetermined patterns in a scanning direction of the opticalsystem, extending directions of the plurality of predetermined patternsbeing oriented in mutually different rotation directions about therotational center.
 11. The flare-measuring method according to claim 10,wherein the arranging of the predetermined pattern further comprisesarranging a plurality of lines of the plurality of predeterminedpatterns arranged in the scanning direction, in a directionperpendicular to the scanning direction.
 12. The flare-measuring methodaccording to claim 10, wherein the first area and the second area arearranged along a line which passes through the rotational center.
 13. Amask pattern-correcting method for correcting a mask pattern, the maskpattern-correcting method comprising: measuring flare information of theoptical system by the flare-measuring method as defined in claim 10; andcorrecting the mask pattern based on a measurement result of the flareinformation.
 14. An exposure method for illuminating a patterning maskwith the radiation and exposing an object with the radiation via apattern of the patterning mask and the optical system, the exposuremethod comprising: measuring flare information of the optical system bythe flare-measuring method as defined in claim 10; correcting thepattern of the patterning mask based on a measurement result of theflare information; and exposing the object with the radiation via theoptical system and the corrected pattern.
 15. The exposure methodaccording to claim 14, wherein the radiation is an EUV light, and thefirst and second areas have reflectivity.
 16. The flare-measuring methodaccording to claim 10, wherein: the predetermined pattern includes aplurality of projection patterns aligned on the mask; and each of theprojection patterns includes the first area, the second area, and theblock area.
 17. The flare-measuring method according to claim 16,further comprising irradiating the radiation onto each of the projectionpatterns while changing an irradiation amount of the radiation todetermine a first irradiation amount EPa provided when an ideal image ofthe block area is projected onto the photosensitive substrate and todetermine a second irradiation amount EPb provided when an image of theblock area is eliminated so as to determine a flare amount (%) from thefollowing expression: (EPa/EPb)×100.